A common misconception is that cataracts only affect the clarity of vision, but the clouding of the eye’s natural lens can also have serious physical consequences. Their progression can lead to a dangerous rise in intraocular pressure (IOP). This elevated pressure can trigger a secondary form of glaucoma, a condition that damages the optic nerve. Understanding this connection between a maturing cataract and elevated eye pressure is important for preserving long-term vision. This article explains how a cataract can mechanically disrupt the eye’s internal fluid dynamics, leading to pressure issues that require prompt medical attention.
Defining Cataracts and Intraocular Pressure
A cataract is the clouding of the eye’s natural lens, which sits behind the iris and pupil. The lens is composed primarily of water and protein. As a person ages, these proteins break down and clump together, causing the lens to become opaque or hazy. This clouding scatters light entering the eye, resulting in blurred vision, glare, and faded colors.
Intraocular pressure (IOP) is the fluid pressure inside the eye, which must be maintained within a specific range for health. The eye constantly produces a clear fluid, called aqueous humor, which circulates within the front part of the eye. This fluid drains out through a meshwork of tissue located in the angle where the iris meets the cornea, known as the drainage angle.
If the production and drainage of this aqueous humor are not balanced, the pressure inside the eye increases. Sustained high IOP can damage the optic nerve, which transmits visual information to the brain. This damage is the definition of glaucoma, and the resulting vision loss is often irreversible. Therefore, managing IOP is important for preventing permanent visual impairment.
The Mechanism of Pressure Elevation
A cataract can cause increased intraocular pressure through two distinct physical mechanisms, both classified as lens-induced glaucoma. The most common mechanism is phacomorphic glaucoma, which involves a physical obstruction of the drainage angle. As the cataract matures, the lens absorbs water and swells, increasing in thickness and volume.
This enlargement pushes the iris forward, which physically narrows the space between the iris and the cornea where the drainage angle is located. When this angle becomes too narrow, or completely closes, the aqueous humor cannot exit the eye properly, similar to a blocked drain. The resulting fluid buildup rapidly increases IOP, leading to an acute angle-closure glaucoma attack.
The second mechanism is phacolytic glaucoma, which occurs when the cataract becomes hypermature. In this stage, the lens capsule—the thin membrane surrounding the lens—can develop microscopic openings. Through these openings, high-molecular-weight lens proteins begin to leak into the aqueous humor circulating in the anterior chamber.
These large protein molecules and debris, including macrophages that engulf the leaked material, clog the delicate trabecular meshwork. This blockage prevents the aqueous humor from filtering out of the eye, causing the pressure to rise. Unlike the mechanical blockage of phacomorphic glaucoma, phacolytic glaucoma is a form of open-angle glaucoma where the obstruction occurs at the cellular level.
Clinical Management and Treatment
Detecting lens-induced pressure elevation often begins with routine monitoring of IOP during comprehensive eye examinations, especially for patients with maturing cataracts. Elevated pressure readings prompt further investigation, which may include gonioscopy to assess the drainage angle and determine the specific type of glaucoma. Early diagnosis is important because sustained high pressure can lead to permanent optic nerve damage.
Definitive treatment for elevated IOP caused by a cataract is the surgical removal of the cloudy lens. This procedure, called phacoemulsification, involves breaking up and removing the cataract and replacing it with an artificial intraocular lens. In cases of phacomorphic glaucoma, removing the enlarged lens immediately relieves the physical crowding in the front of the eye.
Removing the lens deepens the anterior chamber and opens the drainage angle, restoring the natural outflow pathway for aqueous humor. For phacolytic glaucoma, the surgery removes the source of the protein leakage, allowing the drainage system to clear and pressure to normalize. Cataract surgery reduces IOP, with reductions often ranging from 1 to 2 mmHg in eyes with normal pressure.
Before surgery, temporary measures are often necessary to quickly lower acutely high eye pressure and reduce inflammation. This may involve topical eye drops or oral medications to suppress aqueous humor production or increase outflow. Once pressure is medically controlled and inflammation has subsided, cataract extraction proceeds to address the underlying cause.